Thermal shock and hot corrosion resistance of silicon nitride ceramics are investigated in this study. Silicon nitrides are fabricated by nitride pressureless sintering (NPS) process, which process is the continuous process of nitridation reaction of Si metal combined with subsequent pressureless sintering. The results of thermal shock test show it sustains 400MPa of initial strength during test in the designated condition of ${Delta}T=700{sim}25^{circ}C$ up to maximum 4,800 cycles. Hot corrosion tests also reveal that the strength degradation of NPS silicon nitride did not occur at $700^{circ}C$ with an exposure in Ar, $H_2$, Na and K for 1,275 h.